Video report by ITV News Correspondent Juliet Bremner
A tennis player at the Australian Open in Melbourne has said she was "really scared" after being forced to retire from her match due to "poor air quality".
Dalila Jakupovic collapsed during a coughing fit on court.
Poor air quality following ongoing wildfires in the country has impacted a number of players and caused delays to the qualifying stages of the competition.
Authorities have warned air quality in the state of Victoria - of which Melbourne is the capital - would range from moderate to hazardous following months of bushfires.
Footage from ESPN Australia shows Dalila Jakupovic falling to her knees during her match against Switzerland's Stefanie Voegel.
The Slovenian had to be helped off the court, retiring from the match at 6-5 5-6.
Speaking in her post-match press conference, Jakupovic told journalists: "I was really scared that I would collapse. That's why I went onto the floor because I couldn't walk any more".
She added: "I don't have asthma and never had breathing problems. I actually like heat.
"The physio came again and I thought it would be better. But the points were a bit longer and I just couldn't breathe any more and I just fell on the floor.
"It's not healthy for us. I was surprised, I thought we would not be playing today but we don't have much choice."
Another player, Eugenie Bouchard, left the court during her match against China's You Xiaodi complaining of a sore chest but later returned to win.
Former champion Maria Sharapova has also suffered set backs after her warm up match against Laura Siegemundat was suspended as a result of poor air quality.
The Russian pro tweeted on Tuesday complaining of the heat in Australia.
Elsewhere world number six Elina Svitolina tweeted a graph indicating the levels of air pollution in Melbourne and wrote:
"Why do we need to wait for something bad to happen to do an action [sic]".
Organisers have issued a statement stressing "the health and safety of our players, our staff and our fans is our priority."
Australian Open tournament director, Craig Tiley, said last week that he was hopeful the tournament, due to start on 20 January, would go ahead but said air quality would be closely monitored.
He added: "We have experts who analyse all available live data as specific to our sites as possible and consult regularly with tournament officials and, in the case of heat and smoke, medical experts."
On Wednesday Australian Open's Rally for Relief got underway with a one-set finale at the Rod Laver Arena.
A capacity crowd of more than 15,000 spectators watched Roger Federer defeat Australian Nick Kyrgios in a match in aid of wildfire charities.
Tennis Australia said the night helped raise nearly 5 million Australian dollars (£2.6 million) for the victims of recent and ongoing fires in the country.
Other players who took part included Rafael Nadal, Serena Williams, Caroline Wozniacki and Alexander Zverev.
On several occasions, volunteer fire personnel were invited on the court to play against the tennis stars.